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Advanced Taiwan Ocean Prediction System

Tseng, Tsu-Lun - ALL News | 2020-09-07 | Count:16


Title: Path of the momentum from typhoons into the upper ocean


Tropical cyclones as severe weather systems born in the tropical ocean, can cause devastating damages to the coastlines, such as the storm surges. For the response of the upper ocean to the tropical cyclones, the wind can force strong near-inertial current thereby the shear instability mixing. The entrainment of the cold water from the seasonal thermocline due to the turbulent mixing will decrease the sea surface temperature, and then affect the air-sea heat fluxes to the intensification of storms. The measurements taken by the EM-APEX floats under five tropical cyclones, including Frances 2004, Gustav 2008, Ike 2008, Fanapi 2010 and Megi 2010, are used to compute the drag coefficients Cd, which can be regarded as the efficiency for transferring momentum from the storms into the upper ocean. Compared to the conventional parameterization of Cd using the wind speed |U10|, we propose a new parameterization based on the effective wind duration ζ. The Cd(ζ) can largely decrease the scattering of drag coefficient results between different storms, suggesting that the spatial variation of dominant wave direction and duration for forcing the wind waves are both important to the Cd. That is, surface waves play an important role in the path of the momentum from the tropical cyclones into the upper ocean. Future field experiments for observing the surface waves under tropical cyclones are required



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